Ok so you were all spot-on - I'm seeing the exact same flights & same price on AA.com, but booking into domestic First rather than MCE.

Going to cancel the BA booking (free w/in 24 hours) and re-book the same on AA. Ridiculous, but I guess it doesn't change much...means more tricky compensation if any delay I guess, but on the flip-side I can deal with AA direct whch is probably easier than a BA-plated ticket at a US airport which is where issues are more likely.

AA ticket on BA metal - still able to use Avios to u/grade to First if available?